1. Field of the Invention
The invention relates to a semiconductor device in which a semiconductor element having a function such as switching, memory and amplification and another element, mainly one having a function such as photoelectric conversion, are electrically coupled into an integral form.
2. Description of the Prior Art
As is well known, silicon is extensively used as a material for the manufacture of transistors, ICs, LSIs, etc. Since, however, silicon has a forbidden gap of 1.1 eV and has an optical sensitive wavelength region in the near infrared region, it is unsuitable as a material for an element for receiving or emitting visible light.
As the material of an element for receiving or emitting visible light, accordingly, there has been employed a compound semiconductor material having a forbidden gap greater than that of silicon, for example, a group III-group V compound such as GaP or a group II-group VI compound such as CdS. For large-area uses, an amorphous semiconductor material such as Se is employed.
In order to form a solid state imaging device or a solid state display device by disposing the light receiving or emitting semiconductor elements as described above, in an array, a solid state element having a scanning function is required. With present-day technology, however, it is very difficult to form the solid state scanner by employing semiconductor material other than silicon. In general, therefore, a scanning circuit is constructed of a silicon element, and it is electrically connected by wirings with opto-electric or electro-optic transducers formed of a semiconductor material other than silicon. Thus, a solid state imaging device, as shown by way of example in FIG. 1, is formed.
FIG. 1 is a view for explaining the operation of an example of a solid state imaging device. A large number of MOS transistors T.sub.1, T.sub.2, T.sub.3, T.sub.4, T.sub.5 . . . are formed in a silicon substrate S. Photoelectric transducers P.sub.1, P.sub.2, P.sub.3, P.sub.4, P.sub.5, . . . are electrically connected to the source electrodes of the transistors, respectively.
On the substrate S, an integrated scanning circuit K (usually made up of a clock circuit for determining scanning synchronization and a shift register circuit for transferring pulses to the MOS transistors) is formed, by way of which a voltage from a power supply E is successively applied to the gate electrodes G.sub.1, G.sub.2, G.sub.3, G.sub.4, G.sub.5 . . . of the respective transistors.
If, at this time, light is incident on the photoelectric transducers P.sub.1, P.sub.2, P.sub.3, P.sub.4, P.sub.5 . . . , light currents flow from the sources to the drains when a voltage is applied to the gates. Therefore, signals corresponding to the incident light can be successively derived from a common electrode D.sub.0 which is coupled to the drain electrodes D.sub.1, D.sub.2, D.sub.3, D.sub.4, D.sub.5 . . . of the respective transistors.
Where, in such a device, the number of transistors and photoelectric transducers is comparatively small, wirings between the corresponding transistors and photoelectric transducers may be sequentially connected one by one by the thermocompression bonding of metal wires. However, when the number of transistors and photoelectric transducers becomes large, it becomes difficult to carry out such an electrical connection.
It is, accordingly, desirable to affix silicon scanning circuit elements such as transistors and opto-electric or electro-optic transducers onto the same substrate and to form interconnections between the large number of elements at the same time by a photoetching process employing a photoresist.
In the prior-art device, however, a stepped portion exists ordinarily between the silicon element and the opto-electric (or electro-optic) element, between the substrate and the silicon element, between the substrate and the opto-electric (or electro-optic) element, or the like. This brings forth the problem that an interconnection to pass over such a stepped portion is not easilly formed or that when the interconnection is forcibly made, reliability is low due to its easy disconnection. It has therefore been extremely difficult to form practicable interconnections by photoetching.